A method is known for increasing a torque while inhibiting torque ripple in a brushless motor by adjusting the induced voltage of each phase to a trapezoidal waveform in which an odd-order harmonic is superimposed on a 1st order fundamental wave.
However, when a harmonic is superimposed on the induced voltage to obtain a trapezoidal waveform shape of the induced voltage of each phase, since the phase current of each phase has a sine waveform, a peak current value is considered to be difficult to suppress. For this reason, the current that can flow in a brushless motor is restricted and the motor output is accordingly inhibited.
A brushless motor in which the inter-phase induced voltage waveform between two different phases of armature windings is provided with a trapezoidal waveform has been suggested (see, for example, Patent Document 1). In such a brushless motor, as a result of the inter-phase induced voltage waveform between two different phases being provided with a trapezoidal waveform, the phase current has a trapezoidal waveform and the current peak value of the 1st order component contributing to the motor torque can be increased over that of the sine phase current having the same phase current peak value. Therefore, a high torque and high revolution are realized while inhibiting the peak current value.
Patent Document 1: WO 2008/047698